Device for the transmission of calling and clearing signals in long distance telephonic circuits



\2 jm/m a K m m 9 m E O m m L M SIGNALS IN LONG DISTANCE TELEPHONIC CIRCUITS Filed April 27, 1948.

DEVICE FOR THE 'mmsmzssxou OF CALLING AND CLEARING Patented Apr. 27, 1948 2,440,2si DEVICE i on THE 'rimnslvns'sion or oin n-fl ING AND- CLEARING SIGNALS, IN LONG DISTANCE TEIIEPHONIC CIRCUITS Myron. Lebedinsky, Montlucon', .Fi'ance, asisignor to Societe Anonyme dc Telecommunications; Paris, France, a corporation of France. Application necemtei 29, 1945, seriaina 6381103 In France April 22; 1943 v The present invention-pertains to a device for the transmission of calling and clearing signals in long distance telephonic circuits. These si nails are generally transmitted in circuits of this kindby means of alternating currents having a frequency comprised in the band of frequencies used for conversation or call currents, so that the signalling currents behave, n the circuits, in the same m'anner asthe call currents. jv' 'or example, it is the custom to make use, for calling signals of currents of 500 periods per secondand, for clearing signals, of periodical currents, at 500/20, producedb'y a current generator at 500 PMS, the circuit of which isinterrupted and then closed again 20 times per second. At the ends of the -circuits, use is made of apparatus called voice-frequency ringers on two-wire circuitsQor termination sets on four-wire circuits, the object of which is: on the onehand,to transform the signalling currents of voice frequency into currents adapted to operate the corresponding receivers at thetelephojneexchanges, that is, alterhating current of lowfrequency or continuous curren t; on the other hand, to transform a signal emitted by the telephone exchange in the form of a low frequencycurrent into a 500/29 current to be transmittedloy the circuit.

In known devices of this type, the sending of the calling and clearing signals is carried out by means of suitable generators which are connected to the telephonic circuits, said connection being effected in such a manner that the call circuit is. at the moment interrupted. This device however'lias the drawback that the call currents meet, on their .path, relay contacts the qualityof whichm'ay become insufficient by rea-' phonic circuits so as not to cause the latter to be cut off.

According to aform of embodiment of the-invention; this device comprises the elements enabling a; four-wire circuit to be transformed mm atwo-wire circuit in a manner known per se, as well as a group of relaysenablin'g ofn the 9 Claims. (01. ire-44) one hand, ,a low irequency current generator (2511/55.), tobe connected-in parallel across'this two-Wir c c t at. the tim ofsend to ar s he. ex l ia se through the. i comin pair of a signal of voice frequency modulated at low frequency' (500/20): and OniEhe' other hand, a generator of curren o vvo c f equency. to e n:- nectedrm c amel across. theoutsoinspai f the fourewire circuit, at the: time j of sending through the-tWO-rWi e conne t n circuit; 1 t e, e chance: a low frequ ncy: cu rent ,th lco ne cns i thesaid e eratorstot c rcuits e ried-out without interrupt-ion of thelatter. i r

yway of exampleiai rim of embod m n four-Wire termination and-signalling set in accordance with the invention is; described hereafter and is illustrated" in the accompanying drawing. .v 4 i, f

This drawing shoWsi diagrammatically the incomingend to a trunk exchange of a four-wire telephone circuit comprising the incoming pair ifor the call currents proceeding towards this exchangeas W811: as, the outgoing pair 2- ior the call current proceeding from the exchange. In accordance; withthe invention, the termination and signalling set comprises; in the; first place, unea'ns known per se, for transforming the fourwire circuit Z into a two-wire circuit 3 con nectedto'the trunkexchange. These means com-; prise a differential transformer ,4, having three windingsz the line; I is connected to the terminal's oi the Winding i; whilst the-line-Zis connect'ed,"by'tmeans of a transformerfi, to the midpointsoftheotherwindings I and 8-of the dinerential transformer, the-ends of thesewindingsfl and 8' being connected on the one; hand to the circuit 3' and, on't'he'other hand to'a balancing network 9. a s .i

JOn' theincomingline, before a filter [-0, are branched leadsfor connecting to said line an amplifier H for.- amplifyingthe calling and clearing currents. This amplifier receives current at 500720 and actiiates' two/relays l2 and t3; the effect of which", Whentheir respective armaturesj M and [5" are in their operative, position, is to allow a relay i6 t'ocome to the position of, rest, the armature i'l ofwhich in its turn bringsto'the position of rest a relay filthe armature of which closes the circuit of a relay 20; The relay [.8 comprises two other armatures, one of'jwhich 21 causes; when: relay I 6? isin the operative position, the circuit of a relay 22' to close, the armatures or the l'atter23, 23" controlling the connection- 662 my 2 9 wh h jg nergized in the manner explained above at the time a signalling current is sent in line I, comprises two armatures 124, 24' respectively connected to the two leads of the two-wire circuit 3 and movable between two pairs of contacts 21, 2l'28, 28' respectively connected to a line relay 25 and to the circuit 26 of a low frequency current generator (25 P./S.). The energizing of the relay 20 causes the line relay 25 to be disconnected from the line 3 and the circuit 26 of the generator to be connected to said line. This generator thus becomes branched to the line without the latter being sectioned. At the same time, through its armature 5|, the relay 23 actuates the relay 42, which, by means of its armatures 43 and 43, controls the connection between the line I and the differential transformer 4; this connection is then interrupted,

and the pair I is connected to the pair 3 used for through calls. The armature 45 of the relay 42 closes the filter on a resistance 46 to ensure adaptation of the impedance. Likewise, the resistance 41, put in circuit by means of the armature 48 of a relay 49 fed by the lead 53, has for its object to ensure adaptation of the impedance.

A portion of the current at 25 M./S. coming from the circuit 26 of the generator is sent through the two-wire line 3 towards the trunk exchange, where this current causes the signalling apparatus to operate; the other portion of this current, which is transmitted through the two-wire line 3 in the opposite direction to that of the exchange, is sent towards the outgoing circuit 2, but this current is, on the one hand, very much weakened by a condenser 29 mounted in series in the two-wire circuit 3 and, on the other hand, this current at 25 P./S. is not transmitted by the cable and the telephonic repeater parts, so that this portion ofthe current which is not used for controlling the signalling apparatus of the exchange, has no detrimental effect. Moreover, due to the operation of the relay 42 which has connected the pair I to the pair 3, the current at 25 P./S. cannot reach the amplifier l I.

In the case where the signal at 500/20 has to be sent from the trunk exchange into the outgoing circuit 2, a 500/20 current generator 30 is connected to said circuit through the medium of a potentiometer 3|, by means of the armatures 32, 32 of the relay 22, the contacts of these armatures being permanently connected respectively to two leads of the circuit 2. The armature 32"of the relay 22 forms a short-circuit behind the artificial line -5l, thereby preventing the current at 25 P./S. sent by the exchange from mixing with the voice frequency current emitted by the signalling set. The operation of the relay 22 controlling the connection between the generator 30 and the circuit 2 is obtained as follows: a current having a frequency of 25 P./S. is sent from the trunk exchange into the twowire circuits. Through the resting contacts 21, 21' of the armatures 24, 24' of the relay 20, this current is sent through the winding of the relay 25 the armature 33 of which closes the circuit of the relay 22, said circuit being already closed by the armature 2| of the relay l8 which is then at that moment in the operative position. The effect of the operation of the relay 22 is, on the one hand, to apply the armatures 32, 32' of this relay on their contacts and thus to connect the generator 33 with line 2, and, on the other hand, to disconnect, by attraction of the armatures 23, 23"of this same relay, the amplifier H from the circuit I. In this manner, the relays l2, l3, l6 and It can no longer be actuated by a signal coming through the line I which is thus prevented from disturbing the sending of the signal through the circuit 2. Moreover, the armatures l4 and I5 of the relays l2 and [3 open, in their resting position, the circuit of a relay l6 which controls a relay la the armature [9 of which opens, in its operative position, the lead 36 feeding the relay 20. The relays l8 and It therefore play the part of locking relays preventing, during the sending or the reception of a signal, any interference which might be caused by a signal of opposite direction.

This deviceimay also be used for ensuring the transmission of a signal constituted by a nonmodulated current at 500 P./S. arriving through circuit I, the reception of this signal being manifested by applying, to the leads of the two-wire circuit 3, the negative pole of a battery 31 the positive pole of which is connected to earth; this connexion is obtained by means of the lead 38 controlled by the armatures 39 and 40 of the relays l8 and 34 and connected to the mid-point of a winding 4| mounted in parallel on the circuit 3. Contact 40 of the relay 34 which is moved to its working position when the relay is energized closes the circuit 38. The contact 33 of the relay I8 opens the circuit 38 when the relay I6 is deenergized, i. e., when no signal is received through the incoming pair I.

What I claim is:

1. A device for the transmission of voice frequency calling and clearing signals in long distance four-wire telephonic circuits comprising an auxiliary two-wire circuit connected to the trunk exchange, means for connecting said twowire circuitto the four-wire circuit, a low frequency current generator, a generator of voicefrequency signals modulated at low frequency, a relay circuit, means actuated by said relay circuit for connecting said low frequency current generator in parallel with said auxiliary twowire circuit, means connected'to the incoming pair of the four-wire circuit for energizing said relay circuit when receiving a voice frequency signal through said incoming pair, and means actuated by said relay circuit for connecting said generator of voice frequency signals in parallel with the outgoing pair of the four-wire circuit.

2. A device as claimed in claim 1, wherein said means for connecting said auxiliary two-wire circuit to the four-wire circuit comprises a differential transformer.

3. A device as claimed in claim 1, including a filter connected. across the incoming pair of the four-wire circuit, said relay circuit energizing means including a voice-frequency current amplifier connected across the incoming pair ahead of said filter, and a chain of relays actuated by said amplifier, a line relay, the arrangement of said relay circuit actuated means being such that the last relay in said relay circuit disconnects said line relay from said auxiliary two-wire circuit and connects said low frequency generator in parallel with said circuit.

4. A device as claimed in claim 1, wherein said means for connecting said auxiliary two-Wire circuit to the four-wire circuit comprises a differential transformer including a filter connected across the incoming pair of the four-wire circuit, said relay circuit energizing means including a voice-frequency current amplifier connected across the incoming pair ahead of said filter, and a chain of relays actuated by said amplifier, a

actuated means being such that the last relay in controlling said last mentioned relay from said last relay in said relay circuit, said relay thus controlled by said last relay of said relay circuit controlling the connection between the incoming pair and said differential transformer and the connection between the incoming pair and said special pair.

5. A device as claimed in claim 1 including a filter connected across .the incoming pair of the four-wire circuit, said relay circuit energizing means including a voice-frequency current amplifier connected across the incoming pair ahead of said filter and a chain of relays actuated by said amplifier, a line relay, the arrangement of said relay circuit actuated means being such that the last relay in said relay circuit disconnects said line relay from said auxiliary two-wire circuit and connects said low frequency generator in parallel with said circuit, said means for connecting said auxiliary two-Wire circuit to the fourwire circuit comprising a differential transformer, a relay actuated by said line relay, means including said last named relay for connecting said generator of voice-frequency signals modulated at low frequency to the outgoing pair of the four-wire circuit behind said differential transformer.

6. A device as claimed in claim 1 wherein said means for connecting said auxiliary two-wire circuit to the four-wire circuit comprises a differ ential transformer, and including a filter connected across the incoming pair of the four-wire circuit, said relay circuit energizing means including a voice-frequency current amplifier connected across the incoming pair ahead of said filter and a chain of relays actuated by said amplifier, a line relay, the arrangement of said relay circuit actuated means being such that the last relay in said relay circuit disconnects said line relay from said auxiliary two-wire circuit and connects said low frequency generator in parallel with said circuit, a transformer connecting the outgoing pair of the four-wire circuit to said differential transformer, said line relay being energized by being connected to said auxiliary two-Wire circuit when said last relay in said relay circuit is at rest, a relay actuated by said line relay, means including said last mentioned relay for connecting said generator of voice-frequency signals modulated at low frequency to the outgoing pair of the four-wire circuit behind the transformer connecting said outgoing pair of said differential transformer, said last mentioned relay being provided with an auxiliary contact for short-circuiting said outgoing pair at a point whereby there is no mixing of the low frequency and voice-frequency currents.

'7. In a long distance four wiretelephone circuit a trunk exchange provided with a device for the .transmission of voice frequency calling and clearing signals comprising a low frequency generator, a voice frequency receiver provided at the end of the incoming pair, means for actuating said low frequency generator by said receiver when receiving voice frequency signals through the incoming pair, a voice frequency generator provided at the end of the outgoing pair, and means for actuating said voice frequency generator by the low frequency generator and for connecting said voice frequency generator in parallel with the outgoing pair in order to transmit voice frequency signals through said outgoing pair from the trunk exchange.

8. In a long distance four wire telephone circuit a trunk exchange provided with a device for the transmission of voice frequency calling and clearing signals, comprising an auxiliary two Wire circuit, means for connecting said auxiliary two wire circuit at one end to the trunk exchange and for coupling said circuit at its other end both to the incoming pair and to the outgoing pair of the four wire circuit, a low frequency generator, a voice frequency receiver provided at the end of the incoming pair, means controlled by said recaiver whereby said low frequency generator is connected in parallel with said auxiliary two wire circuit when receiving a voice frequency signal through the incoming pair; a voice frequency generator provided at the end of the outgoing pair, means controlled by said low frequency generator whereby said voice frequency generator is connected in parallel with the outgoing pair in order to transmit voice frequency signals through said outgoing pair from the trunk exchange.

9. In a device according to claim 8, a differential transformer for coupling said auxiliary two wire circuit both to the incoming and to the outgoing pairs of the four wire circuit, a filter arranged in the incoming pair, a voice frequency current amplifier connected in parallel to the incoming pair before said filter, a line relay, a chain of relays energized by said amplifier when receiving voice frequency signals through the incoming pair, the last relay of said chain having fixed contacts connected to said line relay and to said low frequency generator respectively and movable armatures connected to said auxiliary two Wire circuit in a manner to disconnect said line relay from said auxiliary two wire circuit and to connect said low frequency enerator to said circuit when energized by said voice frequency amplifier.

MYRON LEBEDINSKY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

